By on December 22, 2017


fuel pump

Paul writes:

Hi Sajeev, I have an opinion/advice question for your column:

I have an ’05 Audi S4 (B7 generation), and this is not a question about this model’s notorious timing chain that so frequently scandalizes car website comment sections.* I have a longstanding issue with fuel pump vibration. It is extremely noisy when it primes, making a rapid clicking or clunking noise that is audible both inside and outside the car. It only lasts for the priming process, and afterwards, the car starts and runs as normal. There is no hesitation in starting, misfiring, or power loss. It is only a noise.

I assumed it was the fuel pump, so I replaced it, but the problem did not go away. I took it to a German car specialist that I’ve used for many years, someone trusted but also somewhat expensive. He confirmed that the pump is not at fault, but suspects that the housing for the pump — which is built into the fuel tank — is broken. There is some kind of vibration dampener assembly that not doing its job and the noise is from the pump rattling the housing around during priming.

Repairing this, according to him, would involve replacement of the entire fuel tank.

This is obviously not a cheap part, and the tank straddles the driveshaft and rear differential, so replacing it would involve dropping both components and that’s beyond my ability to DIY with the tools I have at my disposal. So it would be a very expensive job at a mechanic. Accordingly, I’ve left the problem unfixed for quite some time now.

Should I suck it up and get this fixed? Aside from being unsightly and annoying, it doesn’t seem to be affecting the running of the car. On the other hand, there’s always the possibility that I may be damaging the pump or the fuel tank and setting myself up for an even bigger expense down the road.

Have you ever heard of anything similar to this? I couldn’t find a whole lot online about other B6/B7 owners with this problem. It seems to be a completely aberrant failure and I was thought maybe you had some insight.

* The timing chain problem on these models is completely overblown and can easily be avoided by making sure you change your oil on schedule and maintain the check valves and oil spray nozzle in the heads. The chain slap comes from oil draining out of the heads while the car is parked, slackening the hydraulic chain tensioners until the engine restarts and builds the pressure back up. Audi was smart enough to foresee this issue and build in a pair of check valves designed to maintain oil pressure in the heads while the car was off, but they can fail and stick open over time. Replacing them proactively will keep your chain properly tensioned and avoid the slap issue. I did mine as soon as I started to hear startup noise 25k miles ago and it went away immediately and never returned. Spread the word!

Sajeev answers:

Consider the word spread on the timing chain problem, now get people changing oil at recommended intervals, LOLZ!

Regarding your fuel pump vibration problem, I have an old Fox-body Ford that had a terribly loud aftermarket fuel pump after a terrible conversion from wussy Central-EFI to manly 4-bbl carburetion. The solution was to either to add an isolating rubber bushing/gasket between the pump and the frame (and pray that was enough), or run an old-school mechanical fuel pump off the front of the engine.

But I digress, your Audi has an easy access port under the back seat to eyeball the vibration problem yourself.

I also doubt your vibration damages the fuel tank, and there’s likely a DIY solution.  Sharpen your knives, Best and Brightest, I smell a wrong answer forthcoming. 

Remove the back seat/fuel pump cover, get a mechanic’s stethoscope, and have someone key-on the car to trigger the fuel pump. After reading this thread, I reckon you’ll isolate the noise quickly without removing anything, and hopefully silence the noise with a GENTLE push or pull on the fuel pump top or the retaining trim ring. If so, you know the source of the vibration may lie elsewhere but can be silenced at the point of contact.

See the rubber ring with the little nubs at each end? I bet that’s the place that needs extra silencing initiatives.

And yes, any tech that values their reputation will replace the whole tank, as I only see proper replacements for that big orange gasket (above). Armchair quarterbacking this problem is a bad move, so my notions involving a thin bead of silicone are going out the window. It really depends on the vibration’s location, how the fuel pump (top part) sits inside the recess, how the locking ring operates, etc.

But I will have faith that this is a cheap fix after some NVH diagnostics on your part.

[Images: Shutterstock user Richard Peterson]

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10 Comments on “Piston Slap: The B7’s Bemoaning Fuel Pump?...”

  • avatar

    I would be hesitant to think that something is broken inside the fuel tank since you have replaced your fuel pump and that pump comes as a complete assembly with the plastic basket. I would check the fuel filter because I’ve seen it cause noises and humming when it get clogged. It sits on the bottom of the car so you will not need to interact with the pump assembly at all.

  • avatar

    If it turns out you want to try damping the noise with silicone, look into 3M 5200 marine adhesive/caulk. There are some automotive threads on using it if you search on the name. Caution – in many applications this stuff is irreversible. Once cured, it may never come off. Ever. Not cheap either, about $12 for 3 oz.

  • avatar

    Check for cracked, broken, or disconnected lines/o-rings/seals inside the tank. The pump may be sucking air on start-up. Fuel may drain out of pickup of pump due to above problems over time, maybe hours or overnight.
    I did a quick online check, but was not able to find out if the Audi in question has the dual fuel pump disaster that started in about 1985 models. That system was/is notorious for noise, engine stalls, and no-start troubles.

  • avatar
    Jack Denver

    I don’t know if the widespread timing chain issues with Audi are the ones that killed my ’99 A6 2.8 V6 (non-turbo and underpowered at 200 HP by modern standards but marginally OK by ’99 standards) but what killed mine was the timing chain tensioner. I did all oil changes and replaced the timing belt at recommended intervals. The way this engine worked is that a rubber timing belt transferred the timing from the crank to the top of the engine – the belt drove a toothed wheel which drove a chain which drove the camshafts. The chain was purposely designed with slack and a hydraulic cam chain tensioner moved in and out to advance or retard the valve timing according to ECU command. All well and good in a typically German overly complicated fashion.

    EXCEPT, the tensioner (which BTW was not listed as a maintenance item) applied the tension by means of non-rolling plastic shoes that pressed against the chain as it slid by. How these shoes lasted even as long as they did (a little over 100K miles) was a miracle. The shoes looked like they were made from the kind of plastic that you get in a Happy Meal toy. I would not have used that kind of sliding friction chain tensioner design in a $99 K-Mart 10 speed bike let alone a $34K+ (1999 $ – $50K today) auto. It’s amazing to me that the rubbing of the steel chain did not grind the shoes to nothing even faster than it did.

    Once the shoes failed, the chain jumped a tooth, the engine was an interference design and that was the end of the car and of my loyalty to the Audi brand.

    • 0 avatar

      Totally agreed – I have never understood why Audi (along with other VAG marques) use such substandard parts in their construction of otherwise beautiful cars. The timing chain tensioner issue has turned so many people off from the Audi brand forever. I have always wanted a W8 engine manual trans Audi, but their use of substandard plastic timing chain tensioners (seriously, why??? What else would Audi expect other than every engine to fail prematurely?) made that a non-starter for me. People cant even give these away free nowadays. Thanks VAG!

  • avatar
    SCE to AUX

    I think Audi could have complexified that design a little more, just to bring it up to proper ‘German Engineering’ standards. Sheesh.

    Here’s the obvious: This sort of thing doesn’t happen on ‘cheap’ Korean cars. But I guess the Audi experience is worth it for some folks.

  • avatar

    If this was an EV you wouldn’t have this problem.

    • 0 avatar

      If this was an (Audi) EV, the problem would be something like the auxiliary battery pack cooling pump. Of course, this pump would be made by the lowest bidder, equipped with lowest quality nylon gears and deeply integrated into the battery pack. Naturally, the battery would be positioned in such a way that requires the rear sub-frame to be removed, and the pump would require electronic Vag-Com voodoo to make all the modules talk to each other.

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